1. Field of Invention
The invention relates to an improve structure of a heat dissipation module for BGA (Ball Grid Array) IC (Integrated Circuit) devices, and more specifically to a metal heart dissipation module design for circuit chips encapsulated in an IC device.
2. Related Art
The BGA IC device is a new generation of semiconductor device that has a small volume and many pins. It is made by mounting a cut chip on a substrate with each I/O connecting point of the chip forming electrical communications with the corresponding circuits on the substrate, followed by glue encapsulation and implanting arrayed tin balls on the bottom surface of the substrate. The arrayed tin balls implanted on the bottom of device replace conventional pins. They are formed at designated locations on a circuit board using surface mount technology.
The chip in the foregoing IC device produces a high temperature during operation. The high temperature has to be controlled so that the chip can function normally. In addition to mixing metal materials that help heat conduction into the glue material, another design, shown in FIG. 4, encapsulates a metal heat dissipation module 7, a chip 8, and a substrate 80 in glue 82. The heat dissipation module 7 has an annular base 70 installed on the substrate 80 and over the chip 8. Several supports 71 extending upward from the inner rim of the annular base 70 support a top plate 72 that is higher than wires 81 connecting the I/O connecting points on the chip 8 to those on the substrate 80. The top plate 72 is outside the glue 82 after encapsulation so that the heat produced by the operating chip 8 can be quickly released to the atmosphere through the large area top plate 72 and good heat conductivity of the metal heat dissipation module 7.
Even though the heat dissipation module 7 can provide heat conduction and dissipation for the chip 8, it is hard to make the top plate 72 of the heat dissipation module 7 totally flat as required. Therefore, the module cannot nicely match the mold. Even if the top plate 72 can be made to be exactly flat, it will also deform due to the high temperature. Thus, when the heat dissipation module 7 and the substrate 80 with the chip 8 mounted on the substrate 80 are encapsulated in the mold 83, the glue 82 is likely to flow onto the outer surface of the top plate 72, producing so-called glue overflow. This results in bad appearance of the device. If the length or area of the overflown glue exceeds an allowed range, an additional cleaning procedure is needed. This will increase machining costs and difficulty in manufacturing.
Furthermore, since the top plate 72 of the heat dissipation module 7 is simply flat, as shown in FIG. 5, the total contact surface between the top plate 72 and the air is not a very large area. Thus, the heat dissipation effect is limited.
In view of the drawbacks in the foregoing heat dissipation module for IC devices, the heat dissipation module in accordance with the present invention provides an improved structure for heat dissipation modules for BGA IC devices. The top plate dissipation can match with the mold better, thereby reducing the problem of thermal expansion. It can fully solve the glue overflow problem during encapsulation and ensures that each finished product satisfies the standards, avoiding the need for a second machining. The design can also increase the heat dissipation area for better heat dissipation.
To achieve the foregoing objective, the main technique disclosed herein is that the heat dissipation module has an annular base whose inner rim is greater than the area needed for connection between the chip and the substrate. Several supports extend from the inner rim of the annular base upwards to support a top plate. The top plate is higher than the highest point of the electrical connection between the chip and the substrate. By extending at least one protruding ring on the top surface of the top plate, the heat dissipation module can match the mold better during encapsulation, thereby avoiding the glue overflow problem and increasing the total area for heat dissipation.
FIG. 1 is a perspective view of the heat dissipation module in accordance with the present invention;
FIG. 2 is a cross-sectional side plan view of the heat dissipation module in FIG. 1 used with a BGA IC device;
FIG. 3 is an enlarged cross sectional side plan view of the top plate of the heat dissipation module in FIG. 2;
FIG. 4 is a cross-sectional side plan view of a conventional heat dissipation module used with a BGA IC device; and
FIG. 5 is an enlarged cross sectional side plan view of the top plate of the conventional heat dissipation module in FIG. 4.